The invention relates to ATM (Asynchronous Transfer Mode) systems and particularly to mobility and call control management therein.
Current telecommunication comprises two trends of particular interest: mobile communication and broadband networks. The term broadband typically refers to a bit rate higher than 2 Mbit/s. The term narrowband usually refers to a bit rate of 64 kbit/s or lower. The term wideband occasionally refers to bit rates from 64 kbit/s to 2 Mbit/s. There are at least two (compatible) reasons for the interest in the broadband networks:
1) One broadband bearer shared among several users, few or none of whom need the whole bandwidth alone, can offer advantages concerning the establishment and flexibility of transmission systems.
2) Information to be transmitted over separate transmission channels may demand broadband channels. Users need new high-quality services which, in turn, call for high bit rates. Such services include for example video conferencing, high-speed data transmission etc. A common denominator for these services is multimedia where image, voice and data are integrated into one service.
Owing to its many strengths, ATM (Asynchronous Transfer Mode) is chosen as the data transmission technique in several protocol structures standardized for a B-ISDN (Broadband Integrated Services Digital Network). In this context, the term transmission refers to the use of ATM switching and multiplexing techniques at a data link layer (i.e. an OSI Layer 2, hereinafter referred to as an ATM layer) for transporting end-user traffic from a source to a destination within the network. Virtual connections are set up between the source and the destination, which requires that the network must be provided with switching operations. Signalling and user information are normally transported on different virtual connections at the ATM layer. A virtual connection is identified at the ATM layer by means of a virtual path identifier (VPI) and virtual channel identifier (VCI).
In ATM, information is transported split in fixed-length cells, whereby the number of the cells in a time unit is proportional to the user""s bandwidth requirements. Each 53-octet cell is divided into a 5-octet header and a 48-octet information field as shown in FIG. 2.
The primary purpose of the header is to identify a connection number for a cell sequence that sets up a virtual channel for a particular call. Several virtual paths that are multiplexed in the ATM layer can be connected to the same physical layer (i.e. an OSI Layer 1), whereby each path is identified by an 8-bit VPI at a user-network-interface (UNI) and by a 12-bit VPI at a network node interface. Each path can comprise several virtual channels, each of which is identified by a 16-bit VCI. The header can also comprise other fields, such as a header error control (HEC), a generic flow control (GFC), a cell loss priority (CLP) and a payload type (PT).
The user-network-interfaces UNI between an ATM terminal and an ATM switch (a private UNI) and between private and public ATM networks (a public UNI) together with an associated UNI signalling (and an ATM cell) are specified at least in the following specifications:
[1] ATM User-Network-Interface Specification, version 3.1, ATM Forum, 1994
[2] ATM User-Network-Interface (UNI) Signalling Specification, version 4.0, ATM Forum, July 1996
[3] ITU-T Recommendation Q.2931 (1994) Broadband Integrated services Digital Network (B-ISDN), Digital Signalling System No. 2 (DSS 2), User-Network Interface (UNI) Layer 3 specification for Basic Call/Connection Control. ITU-T.
In mobile networks (PLMN), radio interfaces have conventionally been narrowband interfaces. Transmission systems in the mobile networks have conventionally been implemented by circuit switched connections in a star or tree network configuration. In order to increase the capacity and flexibility of transmission systems, different broadband packet switched transmission systems, such as WO 9400959 and EP 0366342 have also been proposed for mobile networks. EP0426269 introduces a mobile system wherein base stations are connected to ATM network switches by routers. Virtual connections controlled by the base stations are set up between the base stations through the ATM network. Elementary mobility management is based on routing tables maintained in the base stations and in the ATM switches and updated as the subscribers move in the network.
Another potential future trend is that mobile systems have a broadband radio interface. The transmission system of the mobile system should in that case also be a broadband transmission system, a potential alternative thereof being the ATM technique.
A third trend is to introduce wireless data transmission (wireless ATM) and mobility into ATM networks (wireless ATM). However, the problem with this trend is that current B-ISDN and ATM standards in no way support the mobility management, subscriber authentication, call control, etc., required by wireless communication. Introducing these additional features required by wireless communication into the ATM network calls for considerable development and standardization work to be carried out and significant modifications to be made to the existing ATM systems. Implementing wireless ATM is therefore a slow and an expensive process. Such a process conducted by wireless ATM work groups is about to start in the ATM Forum.
An object of the invention is to enable the introduction of wireless data transmission and mobility into an ATM network without significant modifications to the existing ATM networks and standards.
The invention relates to a wireless ATM network comprising mobile stations, base stations and at least one ATM switch, the base stations being connected to the ATM switch by a user-network-interface (UNI). The invention is characterized in that at least one controlling PLMN network element is connected to said ATM switch by the UNI interface to carry out call control and mobility management,
a first permanent ATM virtual channel is provided between said PLMN network element and each base station for transferring call control and mobility management signalling transparently therebetween through the ATM network,
said PLMN network element is arranged to remotely control said ATM switch to switch ATM virtual channels dynamically between the base stations and another point in the ATM network.
The invention also relates to a cellular radio network as claimed in claim 2 comprising mobile stations, base stations, at least one controlling PLMN network element that is responsible for call control and mobility management, and an ATM transmission network comprising at least one ATM switch, the base stations and said controlling PLMN network element being connected to the ATM switch by a user-network-interface (UNI).
The invention also relates to methods for mobility management and call control in a wireless ATM network and in a cellular radio network as claimed in claims 9 and 10.
The invention also relates to an ATM switch element as claimed in claim 12 and to a mobile network element as claimed in claim 18.
According to the invention, wireless base stations are connected to an ATM switch by a UNI interface in an ATM network. At least one controlling network element of a conventional PLMN network, such as a mobile telephone exchange and/or a base station controller is also connected to the ATM network by the UNI interface, the controlling network element being responsible for mobility management and call control. There is a permanent virtual channel (PVC) via said ATM switch between the base station and said at least one controlling cellular network element. Signalling related for example to call control, mobility management and/or radio resource management between a mobile station and the controlling cellular network element is transmitted over the permanent virtual channel. The intermediate ATM switch (ATM switches) forwards the signalling without interpreting it in any way. For the ATM switch, the controlling cellular network element and the base station represent an ATM terminal that can be reached via the UNI interface. Furthermore, there is a permanent virtual channel PVC between said at least one cellular network element and said ATM switch. Said controlling network element uses the second permanent virtual channel for commanding from a remote location the ATM switch to switch a virtual connection between the base station and another point according to the ATM standards. According to the invention, all special network elements and special functions related to wireless communication can be implemented by using the network elements and solutions previously designed for the PLMN networks. Designing special solutions for the wireless ATM is thus avoided. These cellular network elements are connected to the ATM network via a standard UNI interface, but the signalling between the cellular network elements takes place transparently through the ATM network via said permanent virtual connections. Thus, the signalling related to wireless communication does not cause modifications to a standard ATM UNI protocol. The only addition required to the ATM switch is functionality by means of which the controlling cellular network element can manipulate the ATM switch operation via the second permanent virtual connection to switch or release the desired virtual connection.
In a preferred embodiment of the invention, an ILMI (Interim Local Management Interface) is used as the signalling interface between the ATM switch and the controlling cellular network element via the permanent virtual connection of the invention. In the preferred embodiment of the invention, remote controlling the ATM switch from the cellular network element is carried out by using an SNMP (Simple Network Management Protocol). The SNMP protocol already includes features which can be applied to control the switching in the wireless ATM network of the invention. The controlling cellular network element then acts as an SNMP manager, and an ATM node contains an SNMP agent. Remote commands are carried in SNMP protocol data units (PDU).
Alternatively, remote controlling according to the invention may be implemented by using UNI signalling without a permanent logical channel between the PLMN network element and the ATM switch. This, however, requires the current UNI signal to be modified in order to enable the switching to be remotely controlled.